The DMV classifies a truck as "a motor vehicle primarily designed for hauling goods or property and for normal road use."
A truck that is registered under the name of a business is considered commercial and must pay commercial fees.
Note: When the Centennial series started, cars and trucks both started to receive these new plates, so the plate distinction between cars and trucks ended. Now that the Centennial plate run has ended, is is likely that the new E-series plates will be issued to trucks as well. If you spot a [9999 DT] plate on a truck, please contact me.